Automatic propeller pitch control and feather mechanism



April 1966 M. F. COOPER 3,245,475

AUTOMATIC PROPELLER PITCH CONTROL AND FEATHER MECHANISM Filed Sept. 10, 1964 2 Sheets-Sheet l c v IEfLflT/VJ' W/lva DigcT/OA FIG. 3A FIG. 3B F1636 FIG. 30

INVENTOR M17360! F. CQOPEE ATTORN S April 12, 1966 M. F. COOPER 3,245,475

AUTOMATIC PROPELLER PITCH CONTROL AND FEATHER MECHANISM Filed Sept. 10, 1964 2 Sheets-Sheet 2 FIG. 2

INVENTOR MflRCl/S ECOOPZB BY M ATTORNEYS United States Patent i 'AUTOMATIC PROPELLER PITCH CONTROL AND FEATHER MECHANISM Marcus F. Cooper, 596 Ockley Drive, Shreveport, La. Filed Sept. 10, 1964, Ser. No. 395,630 Claims. (Cl. IND-160.15)

The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without the payment to me of any royalty thereon.

Automatic variable pitch propellers for aircraft wherein the pitch is adjusted in response to the control of a governor to vary the load, to thereby maintain the engine speed substantially constant, have come into extensive use. In such a system for a given governor engine speed setting, there is only one airspeed of the aircraft at which the propeller blade airfoil sections will be operating at the most efiicient or optimum angle of attack. Further, for low powered aircraft, the control system becomes very expensive.

In accordance with the present invention, no attempt is made to maintain engine speed constant except that a safe maximum engine speed cannot be exceeded. The entire accent is to provide a propeller pitch control system which maintains the angle of attack of the main propeller blades relative to the incoming airstream at substantially the angle of optimum etficiency.

The invention relates to an improved automatic variable pitch propeller in which an auxiliary propeller, hereinafter called a sensing propeller, responsive to variation in the relative wind, or resultant incoming airstream with respect to the sensing propeller blades initiates rotation of the sensing propeller relative to the main propeller.

The sensing propeller is operatively connected to the pitch changing mechanism of the main propeller blades so that rotation of the sensing propeller relative to the main propeller effects a change in the angle of attack of the propeller blades until a predetermined angle of attack is again attained, the sensing propeller also having blades adjustable in pitch and operatively connected to the pitch adjusting means of the main propeller blades so that the auxiliary blades are changed in pitch in a direction to reduce the angle of the sensing blades with respect to the relative incoming airstream until substantial coincidence occurs.

I am aware that it has been heretofore proposed to vary the pitch of the blades of a variable pitch propeller by employing an auxiliary fixed pitch propeller adapted to rotate in either direction relative to the main propeller in response to the change in the angle of the incoming relative wind, the auxiliary propeller being connected to the mechanism for varying the pitch of the blades of the main propeller. Arrangements of this type tend to cause the main propeller blades to go to either the high or low pitch limits.

I am also aware that it has been proposed to employ a yielding spring means to bias the pitch changing mechanism of a variable pitch propeller in one direction and opposed by a torque developed by a fixed pitch auxiliary propeller acted upon by the relative moving airstream. Or the fixed pitch propeller is employed as a windmill or turbine to generate power to affect pitch change.

The specific features and operation of an automatic variable pitch propeller in accordance with the invention will become apparent by reference to the detailed description hereinafter given when taken in conjunction with the appended drawings in which:

FIG. 1 is a diagram illustrating the aerodynamic operating conditions of an airfoil section of a propeller blade;

acquired through the plane of the propeller. peller airfoil section D traverses a spiral path and in Patented Apr. 12, 1966 FIG; 2 is a plan view partly in section of a propeller.

ice

in accordance with the invention; and

FIG. 3 is a four-part diagram illustrating the operation of a propeller in accordance with the invention under certain flight conditions. The respective parts of the figure are indicated as 3A; 3B; 3C and 3D.

Referring now to FIG. 1, there is depicted a triangular velocity diagram OAB, which represents assumed flight conditions encountered by the airfoil section generally indicated by the reference character D, of an aircraft propeller, the section D having a radius R from the axis of rotation. The leg 0A of the velocity diagram is representative of the rotational velocity V=21rRn where R is measured in feet and n=the engine revolutions per second. The triangleleg AB, represents the velocity of the airstream normal to the plane of rotation of the propeller and is made up of the indicated airspeed V plus /3v which is magnitude of the slip-stream velocity v The proeffect experiences the relative wind along the resultant OB in the direction as indicated by the arrow 0. The angle of the relative wind C to the plane of rotation of the propeller section D, is designated as the angle 5. In order for the airfoil section D to develop lift and hence thrust, it must be inclined in general to the relative wind at a positive angle a which for maximum efficiency should correspond to the angle of maximum value of the liftdrag ratio L/D. In the case of a fixed pitch propeller, the angle a corresponds to the value of the angle of maximum L/ D only for one airspeed and engine revolutions, usually selected to correspond to cruise conditions.

The efficiency of the propeller sections then drops off rapidly on either side of the optimum design point. For any given constant engine speed setting, the conventional automatic governor controlled variable pitch propeller will be similar to a fixed pitch propeller.

Referring now to FIG. 2, a propeller constructed in accordance with the invention is seen to comprise a main hub structure generally indicated by the reference numeral 1 which is suitable internally splined to fit on the splined engine driven shaft 2 and to be driven thereby. The hub 1 is provided with the usual radially extending sockets 3 and 4 which serve to rotatably receive the cylindrical shanks of propeller blades 5 and 6 respectively. The propeller blades 5 and 6 are supported by conventional antifriction bearings (not shown) to permit the blades to be respectively adjusted in pitch about their longitudinal axes by means of gears 7 and 8 fixed respectively to the shanks of blades 5 and 6. The pitch change gears 7 and 8 mesh respectively with pinion gears 9 and 10 which are respectively fixed on the outer ends of shafts 11 and 12 journaled for free rotation by means of suitable bearing means not shown. The shafts 11 and 12 respectively have bevel gears 13 and 14 fixed on their inner ends. The gears 13 and 14 respectively mesh with corresponding bevel gears 15 and 16 respectively formed integral with spur gears 17 and 18 and the gear clusters being free to turn on the respective stub shafts 19 and 20 mounted on the hub structure 1. The spur gears 17 and 18 each mesh with a ring gear 22 cut integral with the inner end of a cylindrical sleeve 23 journaled at its inner end by means of a ball bearing 24 in turn supported on a cylindrical spindle 25, formed as an extension of the propeller shaft 2.

It will be seen that rotation of the sleeve 23 in either direction relative to the supporting spindle 25 will through ring gear 22 and meshing gear train gears 17, 15, 13, shaft 11 and gears 9 and 7 cause propeller blade 5 to be changed in pitch. Similarly rotation of sleeve 23 and ring gear 22 will through gear train elements gears 18, 16,

14, shaft 12 and gears and 8 effect a corresponding pitch change in propeller blade 6. It will be noted that ring gear 22 rotating in one direction will cause gears 7 and 8 and propeller blades 5 and 6 to rotate in opposite directions which is essential. The sleeve 23 forms the principal means for effecting the change in pitch of propeller blades 5 and 6 and the means for rotating the sleeve 23 to effect pitch change will now be described.

The sleeve 23 at its outer end forms a part of an auxiliary propeller hub structure generally indicated by the reference numeral 39. The hub structure 34] is supported at its outer end by means of a combined radial and thrust load bearing 31 mounted on the outer end of the spindle 25 and retained by a nut 32. The hub structure is provided with diametrically opposed bores 33 and 34 which serve to receive the shanks of the respective sensing propeller blades 35 and 36, suitably supported for free rotation about their longitudinal axes by the usual antifriction bearings.

If we assume at this point that the sensing propeller blades 35 and 36 have their pitch angles fixed, it is evident from previous consideration of FIG. 1 that if angle 5 changes due to change in either engine revolutions per minute, or airspeed, or both that the direction of the relative wind with respect to the blades will change. Shift in the relative wind in either direction with respect to the angle of zero lift of the airfoil sections of the blades will give a net lift reaction creating a torque component rotating the sensing propeller in one direction or the other. Rotation of the hub 30 of the sensing propeller in either direction relative to the spindle 25 will cause the sleeve 23 to rotate and affect a change in pitch of the main propeller blades 5 and 6.

In order to make the change in pitch of the main propeller blades proportional ot the angular change in the relative wind from a previous value additional structure associated with the sensing propeller is required and will now be described. As previously described, the sensing propeller blades 35 and 36 are respectively mounted in the hub structure 30 so as to be adjustable in pitch. At their inner ends the shanks of blades 35 and 36 have bevel gears 37 and 38 rigidly secured thereto with the bevel gears each meshing with a bevel gear 40. The bevel gear 40 has integrally formed therewith as a cluster a spur gear 41, the gear cluster being free to rotate on a necked down portion 43 of the spindle 25. The spur gear 41 meshes with a pair of pinion gears 44 and 45 journaled by means of shafts 46 and 47 in a cylindrical cavity 48 of housing 30. The shafts 46 and 47 are parallel to the axis of spindle 25 and rotatable in suitable antifriction bearings carried by the housing and a cover plate 50 thereof. Spur gears 52 and 53 are respectively fixed to shafts 46 and 47 and mesh with a single spur gear 55 which is made fast on the reduced diameter portion 43 of spindle 25 by means of splines, keys or the like not shown.

When the angle of the relative wind experienced by the sensing propeller changes in either direction from the angle of zero lift a lift reaction will be produced giving rise to a torque causing rotation of the sensing propeller hub structure 30 including sleeve 23. Rotation of sleeve 23 will produce a change in pitch of the blades 5 and 6 of the main propeller tending to bring the airfoil sections of the blades into a relation with the changed relative wind such that the blade sections will be set at approximately the angle of best L/D with respect to the relative wind. As soon however as the sensing propeller begins to rotate by windmilling relative to the main propeller to effect pitch change of the main propeller, the sensing propeller will also be rotating in either direction with respect to the spindle 25. Rotation of the sensing propeller housing 30 relative to spindle 25 will cause spur gears 52 and 53 to roll on spur gear 55 acting as a sun gear driving pinion gears 44 and 45 which in turn will rotate spur gear 41 and bevel gear 40 as a unit relative to spindle 25. Rotation of bevel gear 40 will rotate meshing bevel gears 37 and 38 in opposite directions to change the pitch of sensing propeller blades 35 and 36.

If we consider at any instant that a change in the angle 5 FIG. 1, or angle of the relative wind experienced by the blade sections constitutes an error angle, the rotation of the sensing propeller housing 30 and sleeve 23 will effect a change in pitch of the blades of the main propeller toward the new relative wind. As the sensing propeller windmills to effect a change in pitch of the main propeller blades the rotation of the housing 30 thereof relative to the spindle 25 will cause a change of pitch of the sensing propeller blades 35 and 36 in a manner as previously described. The change in pitch of the sensing propeller blades is in the same sense as the change in pitch of the main propeller blades and effective to decrease the error angle. It is preferable to make the airfoil sections of the sensing propeller blades 35 and 36 in the form of symmetrical sections so that the angle of zero lift is zero degrees angle of attack. Further, it is essential that the rates of pitch change of the main and sensing propeller be the same. Under such circumstances, the final equilibrium condition is when the sensing propeller blade sections are substantially aligned with the relative wind and the sensing propeller will then rotate in the same direction and at the same speed as the main propeller and further pitch change will cease. It is further essential that the blade pitch changing mechanism be phased relative to the follow-up pitch changing mechanism for the sensing propeller so that when, for example, a blade section at seventy percent radius of the sensing propeller is aligned with the relative wind that the corresponding airfoil blade section of the main propeller blades be positioned at the angle of attack for best L/D for the particular airfoil section. Since structural considerations make it impractical to have all airfoil sec tions of the main propeller blades with the same maximum thickness to chord ratio and further since inflow velocity is not proportional to the radius of the respective blade sections, all of the blade sections will not uniformly be positioned at the same effective angle of attack with respect to the relative wind so it is assumed that a blade section at seventy percent of the blade radius is representative of the entire blade and a similar assumption is made with respect to the blades of the sensing propeller.

It will be apparent that during flight the sensing propeller serves as a control organ for determining the rate and magnitude of the pitch change of the main propeller blades as the effective pitch angle is varied by change in airspeed, or engine speed, or both. Further, that as pitch change takes place engine speed will be altered in turn varying the thrust which varies the horsepower output, the airspeed and the inflow velocity. Once the sensing propeller senses a change in the angle of the resultant wind it will rotate in a direction and at a rate dependent on the magnitude of the change and will operate through the pitch changing mechanism to change the pitch of the main propeller blades which, in turn, will cause a change in engine revolutions and some change in airspeed and inflow velocity and by feedback will simultaneously change the pitch of the sensing propeller blades. The resultant effect is that an equilibrium position will finally be reached in which at least the mean airfoil sections of the sensing propeller blades will be in alignment with the resultant wind and further windmilling torque on the sensing propeller will cease and no further change in pitch of the main blades will occur and which will leave at least the main propeller blade sections at .7R positioned at the angle of attack of maximum L/D with respect to the final value of the resultant wind.

For consideration of the operation of a propeller in accordance with the invention, reference is made to FIG. 3 for illustration of the various primary flight conditions.

As seen in FIG. 3A which represents the take-off condition, the velocity triangle similar to FIG. 1 has the leg A, representing peripheral velocity of the propeller at a given section, at a maximum While the leg AB representing the sum of the ground speed and inflow velocity is a minimum. The angle 95 is small and the resultant wind C makes a corresponding angle with the plane of rotation of the main propeller. When the engine is started and the aircraft begins take off, the relative wind will strike the blades 35 and 36 of the sensing propeller and cause rotation of the hub 30 thereof and the sleeve 23 relative to the spindle 25. The rotation of the sleeve 23 will be in a direction to reduce the pitch of blades and 6 of the main propeller. With the engine throttle set for maximum power, engine revolutions will increase until a limit is reached dependent on the pitch of blades 5 and 6 reaching a low pitch limit position as determined by engagement of conventional low pitch limit stops, not shown. The relative position of sections of main propeller blade 5 and sensing propeller blade 35 is indicated below the velocity diagram and it will be noted that the blade sections are substantially parallel to each other except for the small additional angle of attack of the main propellerblade and in general alignment with the relative wind C shown in the velocity diagram.

FIG. 3B represents the climb condition where the aircraft has left the ground and accelerated to an airspeed suitable for climb. Since there is an increase in airspeed, the vector AB of the velocity diagram of the figure will be larger than in FIG. 3A and the theoretical pitch angle 5 will increase causing a corresponding shift in the angle of the resultant propeller inflow velocity with respect to the plane of rotation of the propeller. The sensing propeller will accordingly rotate in a direction to increase the pitch of blades 5 and 6 of the main propeller. This increase in pitch will cause an increase in load on the engine with a corresponding decrease in engine revolutions. This decrease in r.p.m. will cause a further increase in angle qb in the velocity diagram and a new resultant wind direction. Pitch change will continue until equilibrium finally is reached with the engine speed reduced and airspeed that for best climb and final theoretical pitch angle larger than for take off condition. The relative position of the sections of main propeller blade 5 and sensing propeller blade 35 for the climb condition are shown below the velocity diagram in FIG. 3B.

When the desired cruise altitude is reached, the pilot will place the aircraft in the level flight attitude and change the throttle to cruise power setting. Accordingly, cruise conditions will correspond to the conditions as outlined in FIG. 3C. The airspeed vector AB of the velocity diagram will increase causing an increase in the theoretical pitch angle at and the sensing propeller will begin rotation relative to spindle 25 in a direction to increase in the pitch angle of blades 5 and 6 of the main propeller causing a further increase in airspeed. The increase in pitch also will load up the engine reducing engine revolutions which will cause a further increase in the theoretical pitch angle 11 A final balance condition will be reached where further pitch change will stop and the relative position of the sections of the main and auxiliary propeller blades 5 and 35 will be as shown below the velocity diagram of FIG. 3C. 7

If the pilot increases or decreases the engine power while maintaining constant airspeed, the sensing propeller will detect such change and will automatically cause the main propeller blades to change toward and maintain the best L/D position with respect to the air flow approaching the main propeller blades. Likewise, while maintaining constant power, if the pilot causes the aircraft to descend or climb, thereby increasing or decreasing the airspeed of the aircraft, the sensing propeller will detect the change in relative angle of the air approaching the propeller blades. This will cause the main propeller blades to change toward and maintain the best 6 L/D position with respect to the air flow approaching the main propeller blades.

If there is a complete engine failure in flight or the pilot cuts the ignition circuit, the engine speed will suddenly decrease with a consequent reduction of the peripheral velocity while the airspeed component remains temporarily constant or increases. This will causethe resultant of the velocity diagram to approach a straight line corresponding with the velocity vector AB and ultimately the vector OR will reach zero. Conditions will then be similar to the feather condition illustrated in FIG. 3D. The changing relative wind will drive the sensing propeller blades 35 and 36 in a direction to change the pitch of the main propeller blades beyond the maximum pitch angle encountered in powered flight and ultimately the sensing propeller blades will come into alignment with the relative wind vector and the blades of the main propeller will be at a small pitch :angle equal to the angle of maximum L/D. In order to prevent the blades of the main propeller being driven beyond the feather position, a mechanical stop (not shown) preferably is employed. The feathered position of the sections of the main propeller blade 5 and sensing propeller blade 35 are as appears below the velocity diagram in FIG. 3D. Where the provision of feathering is not desired, conventional high pitch limit stops may be employed.

I claim:

1. In an automatic variable pitch propeller a main propeller hub, ma-in propeller blades journaled in said hub and adjustable in pitch about their longitudinal axes, pitch changing mechanism in said hub operatively connected to said main propeller blades for varying the pitch angles thereof, means for actuating said pitch changing mechanism comprising an auxiliary propeller mounted for free rotation on said hub, said auxiliary propeller having blades adjustable in pitch, means interconnecting said auxiliary propeller and the pitch changing mechanism of said main propeller, said auxiliary propeller being responsive to variation in inclination of the relative wind experienced by said auxiliary and main propellers to adjust the pitch of said main propeller blades, means responsive to rotation of the auxiliary propeller relative said main propeller to vary the pitch of the blades of the auxiliary propeller until the blade sections of the auxiliary propeller are substantially in alignment with the instant relative wind.

2. In an automatic variable pitch propeller, a main propeller hub, ma-in propeller blades journaled in said hub and adjustable in pitch about their longitudinal axes, pitch changing mechanism in said hub operatively connected to said main propeller blades for varying the pitch angles thereof, said pitch changing mechanism including an input shaft and gearing connecting said input shaft and said main propeller blades, rotation of said input shaft in opposite directions respectively causing increase and decrease in .the pitch of said main propeller blades, an auxiliary propeller dn'vingly connected to said input shaft, said auxiliary propeller being rotatable by the inclination of the relative wind with respect to the blades thereof to effect actuation of the said main propeller blade pitch changing mechanism, said auxiliary propeller having blades adjustable in pitch and means dependent upon rotation of said auxiliary propeller relative to the main propeller hub for adjusting the pitch of the auxiliary propeller blades so that the auxiliary propeller blades are ultimately feathered with respect to the relative incoming airstream.

3. In an automatic variable pitch propeller, main propeller blades adjustable about their longitudinal axes in pitch, pitch adjusting mechanism for varying the pitch of said main propeller blades including a rotatable shaft element, a windmilling propeller operatively connected to said rotatable shaft, said windmilling propeller being responsive to change in the direction of the relative incoming airstrearn, said w-indmilling propeller having blades adjustable in pitch, and means for varying the pitch of said last named blades toward the feathering posi tion with respect to the relative incoming airstream as rotation of said windmilling propeller etfects change in pitch of said main propeller blades.

4. In an automatic variable pitch main propeller, a main propeller hub having main propeller blades journaled therein for variation in pitch about their longitudinal axes, mechanism within said hub operatively connected to said main propeller blades to vary the pitch thereof and including an input shaft, an auxiliary windmilling propeller mounted on said input shaft and adapted to rotate said shaft in either direction relative to said hub in response to shift in the direction of the relative wind, said auxiliary windmilling propeller having blades adjustable in pitch and means interconnecting said main propeller hub and said auxiliary propeller blades such .that rotation of said auxiliary in either direction relative to said main propeller hub will adjust the pitch of the auxiliary propeller blades to be feathered with respect to the relative incoming airstream when the main propeller blades have been adjusted to a predetermined angle of attack with respect to said relative incoming 'airst-ream.

5. In an automatic variable pitch propeller, a main propeller hub, main propeller blades journaled in said hub and adjustable in pitch about their longitudinal axes,

pitch change mechanism in said hub operatively connected to said main propeller blades for varying the pitch angles thereof, power means for energizing said pitch change mechanism including a shaft 'rotatably mounted in said main propeller hub, an auxiliary windmilling propeller mounted on said shaft and rotatable in either direction relative said main propeller hub in response to a shift in the angle of the relative wind with respect to the blades of said auxiliary propeller, said auxiliary propeller having blades adjustable in pitch and means for varying the pitch of the blades of said auxiliary propeller responsive to the amount and direction of rotation of said auxiliary propeller relative the main propeller hub.

References Cited by the Examiner UNITED STATES PATENTS 1,425,922 8/1922 Wesnigk 170-160.21 1,825,768 10/1931 Barbarou 170-160.l5 2,041,789 5/1936 Stalker 170160.15 X 2,113,478 4/1938 Gobereau 170-160.15 2,141,552 12/1938 Ratie 170160.15 2,326,308 8/1943 Reissner 170-160.14

SAMUEL LEVINE, Primary Examiner.

E. A. POWELL, 1a., Assistant Examiner. 

1. IN AN AUTOMATIC VARIABLE PITCH PROPELLER A MAIN PROPELLER HUB, MAIN PROPELLER BLADES JOURNALED IN SAID HUB AND ADJUSTABLE IN PITCH ABOUT THEIR LONGITUDINAL AXES, PITCH CHANGING MECHANISM IN SAID HUB OPERATIVELY CONNECTED TO SAID MAIN PROPELLER BLADES FOR VARYING THE PITCH ANGLES THEREOF, MEANS FOR ACTUATING SAID PITCH CHANGING MECHANISM COMPRISING AN AUXILIARY PROPELLER MOUNTED FOR FREE ROTATION ON SAID HUB, SAID AUXILIARY PROPELLER HAVING BLADES ADJUSTABLE IN PITCH, MEANS INTERCONNECTING SAID AUXILIARY PROPELLER AND THE PITCH CHANGING MECHANISM OF SAID MAIN PROPELLER, SAID AUXILIARY PROPELLER BEING RESPONSIVE TO VARIATION IN INCLINATION OF THE RELATIVE WIND EXPERIENCED BY SAID AUXILIARY AND MAIN PROPELLERS TO ADJUST THE PITCH OF SAID MAIN PROPELLER BLADES, MEANS RESPONSIVE TO ROTATION OF THE AUXILIARY PROPELLER RELATIVE SAID MAIN PROPELLER TO VARY THE PITCH OF THE BLADES OF THE AUXILIARY PROPELLER UNTIL THE BLADE SECTIONS OF THE AUXILIARY PROPELLER ARE SUBSTANTIALLY IN ALIGNMENT WITH THE INSTANT RELATIVE WIND. 